Rivers run dry as drought hits Amazon

Droughts are growing more severe. Has the world's largest rain forest reached its tipping point?

Brazilians cross the muddy bottom of the Rio Negro, a major tributary to the Amazon River, in the city of Manaus, Oct. 26, 2010. (Euzivaldo Queiroz/A Critica/Reuters)

Climate change has been on everyone's minds for much of the year, and not just because of the climate change conference in Cancun. In places like Vietnam, Colombia and Pakistan, it's a matter of battling unpredicatable, extreme weather everyday. Here is one of GlobalPost's greatest hits of 2010, a look at the droughts plaguing the world's largest rainforest.

MUTUM, Brazil — A motorboat barreling through the night up a shallow Amazon stream could only beat the odds for so long.

Just after 9 p.m., the aluminum canoe slammed to a halt with the sound of a thunderclap. Passengers and cargo lurched into the air. Shouts of surprise, profanity and a man-sized splash echoed in the dark.

A swift lesson on Newtonian physics and the risks of night boating had been delivered by a large, semi-submerged tree.

The mishap demonstrated what everyone in this remote corner of the Brazilian jungle had been saying for days.

The world’s largest rain forest was dangerously dry, and may well be drying out.

October marked the end of one of the worst Amazon droughts on record — a period of tinder-dry forests, dusty cropland and rivers falling to unprecedented lows. Streams are the highways of the deep jungle and they’re also graveyards for dead trees, usually hidden safely under fathoms of navigable water.

But not this year, and the drought’s significance extends far beyond impeded boats.

While the region has seen dry spells before, locals and experts say droughts have grown more frequent and severe. Scientists say there’s mounting evidence the Amazon's shifting weather may be caused by global climate change.

The world’s largest rain forest has long been a bulwark of hope for a planet troubled by climate change. Covering an area the size of the continental United States, the Amazon holds 20 percent of Earth’s fresh water and generates a fifth of its oxygen. With the planet's climate increasingly threatened by surging carbon emissions, the Amazon has been one of the few forces keeping them in check. But the latest scientific evidence suggests the forest may be unable to shield us from a hotter world.

“Every ecosystem has some point beyond which it can’t go,” said Oliver Phillips, a tropical ecology professor at the University of Leeds who has spent decades studying how forests react to changing weather. “The concern now is that parts of the Amazon may be approaching that threshold.”

Phillips led a team of dozens of researchers who studied the damage caused by a severe 2005 drought to trees and undergrowth at more than 100 sites across the Amazon. His findings, published in the journal Science, are troubling.

Through photosynthesis, the rain forest absorbs 2 billion tons of atmospheric carbon dioxide each year. But the 2005 drought caused a massive die-off of trees and inverted the process. Like a vacuum cleaner expelling its dust, the Amazon released 3 billion tons of carbon dioxide in 2005. All told, the drought caused an extra 5 billion tons of heat-trapping gases to end up in the atmosphere — more than the combined annual emissions of Europe and Japan.

It still remains to be seen whether the rain forest’s ability to absorb greenhouse gases has been permanently harmed. “We can’t say for sure — it could be happening now,” Phillips said. “Often you don’t know you’ve passed a turning point until you’ve already passed it.”

Phillips said he’s worried about yet another drought following so closely after the last. Along the edge of the forest in Peru and Bolivia, there were more fires this year than any year on record, he said, along with reports of substantial damage to plants in the normally wet northwestern Amazon.

“The humid tropical forests have evolved at pretty high temperatures but there’s a temperature at which you don’t see them on the planet,” said Greg Asner, an ecologist at the Carnegie Institution for Science. “And some tropical forests in the world now are starting to be exposed to temperatures they’ve never experienced.”

(Courtesy Greg Asner.)

Asner recently completed a study of world rain forests showing just how extensive the damage could be. He took 16 leading models for predicting the next century of climate change and essentially created a map — showing hotspots where they all agreed rising greenhouse gases would substantially change the forest.

He found that higher temperatures and shifts in rainfall could leave as much as 37 percent of the Amazon so radically altered that the plants and animals living there now would be forced to adapt, move or die. When other man-made factors like logging are taken into account, the portion of affected forest could be as high as 81 percent.

Asner said melting polar ice sheets aren’t the only climate change sentinels out there. The world’s largest rain forest — drained, drying, sometimes burning — is on the front lines, too, and just as threatened.

“I hate to pit myself against the polar bears,” he said. “But we’re talking about the Amazon, the majority of the biodiversity on the planet is in the humid tropical forests.”

Locals call the Amazon’s annual dry spells “the burning season,” named for the forest fires landholders regularly set to make room for crops and cows. In past decades, fires kindled on the jungle’s edges burned themselves out once they advanced a few yards into permanently damp virgin forest.

But that changed with the 2005 drought, said Foster Brown, an environmental scientist at the federal university in the Brazilian state of Acre.